Purpose :
To investigate the role of near work and time outdoors and their interaction in prevalent myopia and longitudinal change in refraction and axial length in Australian schoolchildren.

Methods :
The Sydney Adolescent Vascular and Eye Study (SAVES) followed up children from the Sydney Myopia Study (SMS), a population-based random cluster sample of 55 schools in Sydney. Children at baseline were in two age cohorts; 6 years (n=1765) and 12 years (n=2353) who were followed up 5-6 years after initial examination (follow-up 51%). Children underwent a comprehensive ocular examination including, cycloplegic autorefraction (cyclopentolate 1%, Canon RK-F1) and ocular biometry (IOLMaster). The impact of near work and time outdoors obtained by questionnaire, on spherical equivalent refraction (SER), prevalent myopia (≤-0.5 dioptres (D)) and axial length was analysed.

Results :
Time spent in near work and outdoors was poorly correlated in both the younger (r=0.16) and older cohort (r=0.03). In the older cohort, children who spent greater time in near work had a more myopic SER at both baseline (p<.0001) and follow-up (p=0.001). Conversely, children who spent greater time outdoors had a significantly less myopic SER at baseline (p<.0001) and follow-up (p<.0001). Children who combined low time outdoors (<14 h/week) with high amounts of near work (>25.5 h/week) had the most myopic baseline (-0.18D) and follow-up SER (-0.60D). Comparatively, children who spent high time outdoors and low time in near work (<17.5 h/week) had a more hyperopic SER at baseline (0.73D, p<.0001) and follow-up (0.41D, p<.0001). However, there was no significant difference in SER between children who performed either high or low amounts of both time outdoors and near work either at baseline (p=0.5) or follow-up (p=0.7). When near work time exceeded time outdoors, children had greater odds of myopia at baseline (OR 2.69, 95% CI 2.06-3.53) and follow-up (OR 1.94, 95% CI 1.44-2.62). These children also had significantly greater change in SER towards myopia (β -0.116, p=0.001) and axial length growth (β 0.056, p<.0001). Similar trends were observed for the younger cohort.

Conclusions :
Near work and outdoor time are well known to be associated with myopia. Previously reported inconsistencies in the relationship between myopia and near work could be attributed to the role of time spent outdoors, suggesting that these factors should be considered in combination.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.